The present disclosure relates to an airbag provided with an open-and-close type vent and a member for limiting a discharge of the gas from the vent. More specifically, it relates to an airbag constructed in such away that the vent is closed or opened by a small amount until an occupant is brought into contact with an occupant-facing surface of the expanded airbag, and the vent is opened or opened by a large amount when the expanded airbag is compressed by the occupant contacting the airbag. Further, the present invention relates to an airbag apparatus provided with the airbag.